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At least 505 records · Page 28Linked to original sources
PubMed2005

Detecting extra dimensions with gravity-wave spectroscopy: the black-string brane world.

Using the black string between two branes as a model of a brane-world black hole, we compute the gravity-wave perturbations and identify the features arising from the additional polarizations of the graviton. The standard four-dimensional gravitational wave signal acquires late-time oscillations due to massive modes of the graviton. The Fourier transform of these oscillations shows a series of spikes associated with the masses of the Kaluza-Klein modes, providing in principle a spectroscopic signature of extra dimensions.

Journal Article↗
PubMed2005

Form of growing strings.

Patterns and forms adopted by nature are often the results of simple dynamical paradigms. Here we show that a growing self-interacting string attached to a tracking origin, modeled to resemble nascent polypeptides in vivo, develops helical structures which are more pronounced at the growing end. We also show that the dynamic growth ensemble shares several features of an equilibrium ensemble in which the growing end of the polymer is under an effective stretching force. A statistical analysis of native states of proteins shows that the signature of this nonequilibrium phenomenon has been fixed by evolution at the C terminus, the growing end of a nascent protein. These findings suggest how evolution may have built on the properties of a generic nonequilibrium growth process in favoring helical structures in nascent chains.

Biomimetic Materials↗
PubMed2005

Nonequilibrium relaxation of an elastic string in a random potential.

We study the nonequilibrium motion of an elastic string in a two dimensional pinning landscape using Langevin dynamics simulations. The relaxation of a line, initially flat, is characterized by a growing length L(t) separating the equilibrated short length scales from the flat long distance geometry that keeps a memory of the initial condition. We show that, in the long time limit, L(t) has a nonalgebraic growth with a universal distribution function. The distribution function of waiting times is also calculated, and related to the previous distribution. The barrier distribution is narrow enough to justify arguments based on scaling of the typical barrier.

Journal Article↗
PubMed2005

Black holes in many dimensions at the CERN Large Hadron Collider: testing critical string theory.

We consider black hole production at the CERN Large Hadron Collider (LHC) in a generic scenario with many extra dimensions where the standard model fields are confined to a brane. With approximately 20 dimensions the hierarchy problem is shown to be naturally solved without the need for large compactification radii. We find that in such a scenario the properties of black holes can be used to determine the number of extra dimensions, . In particular, we demonstrate that measurements of the decay distributions of such black holes at the LHC can determine if is significantly larger than 6 or 7 with high confidence and thus can probe one of the critical properties of string theory compactifications.

Journal Article↗
PubMed2006

Supersymmetric standard model from the heterotic string.

We present a [FORMULA: SEE TEXT] orbifold compactification of the E8xE8 heterotic string which leads to the (supersymmetric) standard model gauge group and matter content. The quarks and leptons appear as three 16-plets of SO(10), whereas the Higgs fields do not form complete SO(10) multiplets. The model has large vacuum degeneracy. For generic vacua, no exotic states appear at low energies and the model is consistent with gauge coupling unification. The top quark Yukawa coupling arises from gauge interactions and is of the order of the gauge couplings, whereas the other Yukawa couplings are suppressed.

Journal Article↗
PubMed2006

Generating the curvature perturbation at the end of inflation in string theory.

In brane inflationary scenarios, the cosmological perturbations are supposed to originate from the vacuum fluctuations of the inflaton field corresponding to the position of the brane. We show that a significant, and possibly dominant, contribution to the curvature perturbation is generated at the end of inflation through the vacuum fluctuations of fields, other than the inflaton, which are light during the inflationary trajectory and become heavy at the brane-antibrane annihilation. These fields appear generically in string compactifications where the background geometry has exact or approximate isometries and parametrize the internal angular directions of the brane.

Journal Article↗
PubMed2006

Inflation, dark matter, and dark energy in the string landscape.

We consider the conditions needed to unify the description of dark matter, dark energy, and inflation in the context of the string landscape. We find that incomplete decay of the inflaton field gives the possibility that a single field is responsible for all three phenomena. By contrast, unifying dark matter and dark energy into a single field, separate from the inflaton, appears rather difficult.

Journal Article↗
PubMed2005

Building kernels from binary strings for image matching.

In the statistical learning framework, the use of appropriate kernels may be the key for substantial improvement in solving a given problem. In essence, a kernel is a similarity measure between input points satisfying some mathematical requirements and possibly capturing the domain knowledge. In this paper, we focus on kernels for images: we represent the image information content with binary strings and discuss various bitwise manipulations obtained using logical operators and convolution with nonbinary stencils. In the theoretical contribution of our work, we show that histogram intersection is a Mercer's kernel and we determine the modifications under which a similarity measure based on the notion of Hausdorff distance is also a Mercer's kernel. In both cases, we determine explicitly the mapping from input to feature space. The presented experimental results support the relevance of our analysis for developing effective trainable systems.

Algorithms↗
PubMed2003

String matching techniques for high-level primitive formation in 2-D vascular imaging.

This paper deals with a so-called "intermediate" description, in other words, the formation of high-level primitives in angiographies. The method is based on an attributed string matching technique capable to capture the shape similarities between low-level primitives (i.e., vessel contours and centerlines). After designing a multiparametric cost function, we propose a multiline pairing algorithm. In order to objectively evaluate its performances, results are first provided on simulated data and then on a set of coronarographic images, where it is shown that anatomically coherent entities like vessel segments and branches can be built, "objects" that can be further individually analyzed for clinical purpose.

Algorithms↗
PubMed2001

Frequencies of amino acid strings in globular protein sequences indicate suppression of blocks of consecutive hydrophobic residues.

Patterns of hydrophobic and hydrophilic residues play a major role in protein folding and function. Long, predominantly hydrophobic strings of 20-22 amino acids each are associated with transmembrane helices and have been used to identify such sequences. Much less attention has been paid to hydrophobic sequences within globular proteins. In prior work on computer simulations of the competition between on-pathway folding and off-pathway aggregate formation, we found that long sequences of consecutive hydrophobic residues promoted aggregation within the model, even controlling for overall hydrophobic content. We report here on an analysis of the frequencies of different lengths of contiguous blocks of hydrophobic residues in a database of amino acid sequences of proteins of known structure. Sequences of three or more consecutive hydrophobic residues are found to be significantly less common in actual globular proteins than would be predicted if residues were selected independently. The result may reflect selection against long blocks of hydrophobic residues within globular proteins relative to what would be expected if residue hydrophobicities were independent of those of nearby residues in the sequence.

Alkyl and Aryl Transferases↗
PubMed1992

Ligature versus purse string for surgical stapled anastomoses.

Intraluminal circular stapling in gastrointestinal surgery requires a purse string suture which secures the bowel around the anvil of the head of the stapling gun before firing. An alternative method of securing the bowel around the anvil is described.

Anastomosis, Surgical↗
PubMed2005

Phosphorylation of cysteine string protein in the brain: developmental, regional and synaptic specificity.

Protein phosphorylation modulates regulated exocytosis in most cells, including neurons. Cysteine string protein (CSP) has been implicated in this process because its phosphorylation on Ser10 alters its interactions with syntaxin and synaptotagmin, and because the effect of CSP overexpression on exocytosis kinetics in chromaffin cells requires phosphorylatable Ser10. To characterize CSP phosphorylation in the brain, we raised phosphospecific antibodies to Ser10. Western blotting revealed that the proportion of phosphorylated CSP (P-CSP) varies between distinct brain regions and also exhibits developmental regulation, with P-CSP highest early in development. Immunohistochemical analysis of the cerebellar cortex revealed a novel pool of P-CSP that did not colocalize with synaptic vesicle markers during early development. Strikingly, in the adult cerebellar granular layer P-CSP was highly enriched in a subset of glutamatergic synapses but undetectable in neighbouring GABA-ergic synapses. In view of the functional consequences of CSP phosphorylation, such differences could contribute to the synapse-specific regulation of neurotransmitter release.

Aging↗
PubMed2002

Enhancement of presynaptic calcium current by cysteine string protein.

The isolated chick ciliary neuron calyx synapse preparation was used to test cysteine string protein (CSP) action on presynaptic N-type Ca(2+) channels. Endogenous CSP was localized primarily to secretory vesicle clusters in the presynaptic nerve terminal. Introduction of recombinant CSP into the voltage clamped terminal resulted in a prominent increase in Ca(2+) current amplitude. However, this increase could not be attributed to a change in Ca(2+) channel kinetics, voltage dependence, prepulse inactivation, or G protein inhibition but was attributed to the recruitment of dormant channels. Secretory vesicle associated endogenous CSP may play an important role in enhancing Ca(2+) channel activity at the transmitter release site.

Animals↗
PubMed2001

Estimation of broadband acoustic power due to rib forces on a reinforced panel under turbulent boundary layer-like pressure excitation. I. Derivations using string model.

This paper shows that, when the attachment forces on a rib-reinforced panel subjected to turbulent boundary layer (TBL) excitation can be considered to radiate independently, the rib-related acoustic power in a broad (e.g., one-third octave) frequency band can be estimated as the product of the average mean-squared force, the real part of the radiation admittance of an attachment force, and the number of ribs. Using a simple model of a string with point mass or spring attachments, an approach is developed for estimating the average mean-squared force in broad frequency bands. The results are in a form that can be applied to ribbed plates and shells. The following paper establishes the condition under which the ribs can be considered to radiate independently, and presents the results of validating calculations for steel plates in water.

Journal Article↗
PubMed2002

Grazing instabilities and post-bifurcation behavior in an impacting string.

A theoretical and experimental investigation of the nonlinear dynamic response of a periodically excited string subject to a knife-edge amplitude restraint is presented. The amplitude restraint creates an impact condition as the amplitude of the response grows. The focus of this work is on the influence of a grazing instability; this zero-velocity impact event leads to complicated, post-bifurcation behavior ranging from multifrequency, periodic motion to chaos. In addition to looking at the response numerically, parameter combinations leading to an incidence of grazing are clearly identified in the excitation force excitation frequency parameter space using a multiple scales perturbation analysis. Modeling issues, numerical difficulties, and experimental limitations are also discussed.

Motion↗
PubMed1995

Increased cortical representation of the fingers of the left hand in string players.

Magnetic source imaging revealed that the cortical representation of the digits of the left hand of string players was larger than that in controls. The effect was smallest for the left thumb, and no such differences were observed for the representations of the right hand digits. The amount of cortical reorganization in the representation of the fingering digits was correlated with the age at which the person had begun to play. These results suggest that the representation of different parts of the body in the primary somatosensory cortex of humans depends on use and changes to conform to the current needs and experiences of the individual.

Adult↗
PubMed2001

Natural communities of novel archaea and bacteria growing in cold sulfurous springs with a string-of-pearls-like morphology.

We report the identification of novel archaea living in close association with bacteria in the cold (approximately 10 degrees C) sulfurous marsh water of the Sippenauer Moor near Regensburg, Bavaria, Germany. These microorganisms form a characteristic, macroscopically visible structure, morphologically comparable to a string of pearls. Tiny, whitish globules (the pearls; diameter, about 0.5 to 3.0 mm) are connected to each other by thin, white-colored threads. Fluorescent in situ hybridization (FISH) studies have revealed that the outer part of the pearls is mainly composed of bacteria, with a filamentous bacterium predominating. Internally, archaeal cocci are the predominant microorganisms, with up to 10(7) cells estimated to be present in a single pearl. The archaea appear to be embedded in a polymer of unknown chemical composition. According to FISH and 16S rRNA gene sequence analysis, the archaea are affiliated with the euryarchaeal kingdom. The new euryarchaeal sequence represents a deep phylogenetic branch within the 16S rRNA tree and does not show extensive similarity to any cultivated archaea or to 16S rRNA gene sequences from environmental samples.

Archaea↗